The present invention is related to digital data transmission methods and apparatus and, more particularly, to a novel method and apparatus for data transmission using chirped frequency-shift-keying modulation.
Data communications over media (such as power lines and the like) having severe noise characteristics presents unique problems. Data transmission over such media suffer from Gaussian noise as well as corruption by unusual noise phenomena, such as high voltage spikes (caused by switching transients) and CW carriers arising from other communications equipment and other sources. Such noise sources adversely affect signal-to-noise ratio and often lead to unacceptably high error rates. Most power line data communication systems concentrate primarily on Gaussian noise reduction, even though such Gaussian noise is not the major noise phenomena typically observed in power line communications. One modulation scheme commonly used for data communications is frequency-shift-keying (FSK) modulation. With optimal receiver design, the FSK technique can be relatively successful and immune to Gaussian noise. Use of FSK modulation is, however, very highly sensitive to CW interference at a few specific frequencies, the occurrence of which CW signals causes a jamming effect and often prevents successful communication. Further, schemes for transmitting FSK modulated data signals often require that the data be transmitted at relatively low bit rates, often at harmonic, or subharmonic, relationships to the power line frequency. It is therefore highly desirable to provide a modulation form capable of allowing data transmission of many hundreds of bits per second, over a noisy media, such as the power line, which media may have undesirable transient and continuous frequency components, while maintaining a relatively low error rate for such data transmission.